1. Field of the Invention
This invention relates to a joint assembly for sealingly connecting the ends of a pair of sheet metal duct sections and more particularly to a joint assembly that includes a pair of frame members having flange portions secured to each other by angular corner pieces.
2. Description of the Prior Art
U.S. Pat. No. 3,712,650 discloses a flange connection for connecting the ends of rectangular air conditioning ducts that includes flange portions having a horizontal leg portion secured to the end portion of the duct and a vertical channel shaped leg for receiving the arms of an angular corner piece. A wall of the horizontal flange portion has a sloping intermediate portion that permits visual access to the bend areas between the adjacent walls of the duct and the ends of the duct walls.
The angular corner pieces have arm portions that extend into an opening in the vertical channel sloped flange. The arm portions are so dimensioned vertically that the lower surface of the arms abut the lower wall of the horizontal flange. With this arrangement, the end of the duct wall abuts or rests against a surface of the corner piece arm extending into the channel shaped opening.
Another joint assembly for connecting the ends of a pair of ducts is disclosed in German Application No. P 25 56 167 filed Dec. 13, 1975, and includes a plurality of flange portions secured to the ends of the ducts and angular corner pieces positioned in vertically extending channel shaped openings in the respective flange portions to form a generally rectangular frame secured to the ends of the ducts. The flange portions each have a generally horizontal duct receiving leg and a vertical channel shaped leg. The duct receiving leg portion has a longitudinal opening for receiving the duct end walls and one wall of the vertically extending channel shaped leg portion has an inturned or inwardly rebent portion that forms longitudinally an extending lip spaced from the lower wall of the horizontal duct receiving leg. The duct end portion is arranged to extend into the space between the longitudinally extending lip and the lower wall of the horizontal duct receiving leg. In position, the duct end wall abuts the inner surface of the outer vertical wall of the upstanding channel shaped leg. The arm of the corner piece is arranged to extend into the opening above the inturned lip so that the corner piece arm portion is spaced from the duct end wall by the inturned lip portion. The corner pieces have arms with a curved configuration so that pairs of facing arms in adjacent frames are intended to exert a joinder pressure on the respective frames when the corner pieces are bolted to each other.
In the above joint assemblies, the duct end walls abut either the arms of the corner pieces or abut the inner surface of the frame channel shaped leg portion outer vertical wall. Where the end of the duct wall rests against the arm of the corner section, a space is provided between a substantial portion of the outer vertical wall of the channel shaped leg and the end of the duct wall. Where the end of the duct wall is positioned in the space between the inturned lip and the horizontal bottom wall, the duct end wall abuts the portion of the vertical wall of the frame section between the lip and the horizontal bottom wall. In either instance, irregularities on the surface of the duct or on the surface of the frame portions permit leakage of the air from the duct through the flange connection. Positioning gasket material on the outer surface of the frame portions does not eliminate this air leakage since the leakage is occurring within the frame portions and around the duct end wall.
Another problem encountered with the joint assemblies of the prior art is the inability to compensate for the variations in the gauge or dimension of the sheet metal forming both the duct and the frame flange portions. For example, a 20 gauge duct is commercially acceptable if it has a dimension of between 0.906 and 1.106 millimeters. In certain instances, there will be a variation of 0.2 millimeters between the various metal surfaces forming the duct and joint assembly and it is readily apparent with such a variation that air leakage is likely to occur.
Both the duct members and the frame members are galvanized and have an irregular surface caused by the galvanizing process so that the thickness of the sheet metal can vary plus or minus 10 percent. Where there are three layers of sheet metal, as for example in the above discussed joint assemblies, the error increases to plus or minus 30 percent of the sheet metal thickness. Again, it is readily apparent that leakage between the duct and the joint assembly is likely to occur.
In the embodiment where an inturned lip is formed in the outer wall of the vertical leg above the lower wall of the horizontal leg, the distance between the lip and the lower wall is so dimensioned as to fit only one gauge of sheet metal. The frame sections having this fixed dimension cannot be utilized with ducts having different metal thickness.
There is a need for a joint assembly that may be utilized with ducts of different thickness and capable of providing an effective seal between the duct end wall and the inner surface of the flange sections.